Tomographic systems for determining characteristics of inhomogenous specimens using guided electromagnetic fields

ABSTRACT

A system for determining characteristics of a specific region within an inhomogeneous dielectric specimen by guiding propagation of electric fields through the inhomogeneous dielectric specimen is provided herein. Various embodiments include at least one source of electromagnetic energy for generating electromagnetic waveforms, the electromagnetic waveforms comprising electric fields propagating along a prescribed path that defines a series of spatial regions through which the electric fields propagate. In some embodiments the prescribed path includes electric field modulating elements that determine a rate of electric field propagation along the prescribed path. Some embodiments include a plurality of conductors for guiding the electric field propagation through an inhomogeneous dielectric specimen in the prescribed path, the electric fields spanning between two or more of the plurality of conductors as the electric fields propagate along the prescribed path. In some embodiments the plurality of conductors are external to the inhomogeneous dielectric specimen.

RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 16/378,425, filed Apr. 8, 2019, titled “Tomographic Systems andMethods for Determining Characteristics of Inhomogenous Specimens UsingGuided Electromagnetic Fields” which claims the benefit of U.S.Provisional Patent Application Ser. No. 62/662,594, filed Apr. 25, 2018,titled “Tomographic Systems and Methods for Determining Characteristicsof Inhomogenous Subjects Using Guided Electromagnetic Waves” and U.S.Provisional Patent Application Ser. No. 62/781,846, filed Dec. 19, 2018,titled “Method to Localize Measurement of Dielectric Characteristics toa Region within Inhomogeneous Dielectrics.” The aforementioneddisclosures are hereby incorporated by reference herein in theirentireties including all references cited therein.

FIELD OF INVENTION

The present technology pertains to interrogation systems for determiningcharacteristics and/or contents of subjects. In particular, but not byway of limitation, the present technology provides interrogation systemsfor determining characteristics and/or contents of dielectric specimens.

BACKGROUND

The approaches described in this section could be pursued, but are notnecessarily approaches that have previously been conceived or pursued.Therefore, unless otherwise indicated, it should not be assumed that anyof the approaches described in this section qualify as prior art merelyby virtue of their inclusion in this section.

Electrical impedance, electrical capacitance, and microwave tomographyhave the potential to become powerful tools in the fields of medicine,security, and manufacturing and other fields that would benefit from thewealth of diagnostic information that can be gleaned from materials'dielectric properties. Unlike X-ray or ultrasound measurements thatprimarily indicate materials' density, dielectric properties can beunique to individual materials and can be used to, for example, identifyspecific tissues or tumors, or distinguish between explosives andfoodstuffs. To date, these dielectric imaging techniques have foundlimited use in boutique diagnostics or in specific situations thatpermit dielectric measurements to be made.

Materials' dielectric properties are not readily resolved to specificspatial regions because dielectric structures can bend, contort,reflect, and diffract the propagation of electromagnetic fields innon-linear ways, which obscures both their spatial position andunderlying dielectric characteristics.

The path of an electromagnetic field through a subject (i.e. specimen)under study will vary according to the frequency or, more generally, therate of change of the field. In static conditions, or where wavelengthsare an order of magnitude or more longer than the dielectric structuresunder investigation, the impedance characteristics of the subject understudy will determine the paths of the current—fields will be drawn intothe material of lowest impedance. As the frequency increases, however,propagation will take on more ray-like behaviors, and propagation willbe dominated by the material of highest propagation velocity.

Traditionally, these two regimes are approached differently.Low-frequency or static techniques like electrical impedance tomography(EIT) or electrical capacitance tomography (ECT)—often called soft-fieldtomography because the bending and curving of the fields contrasts withthe hard-field or straight line of X-rays through an object—apply anarray of electrodes to the surface of an object under study andsequentially apply currents through pairs of electrodes to map outequipotential lines. A computer algorithm then iterates through thepossible impedances of regions to match the equipotential curvesmeasured in the data.

Low-frequency or static EIT/ECT fields can greatly obscure internaldetail, especially at appreciable distance from a dielectric structure,because the fields tend to smooth out with distance. Static techniquesalso struggle with multi-layer structures—a key reason why EIT/ECTelectrodes are directly applied to an object under study because an airgap would add a high impedance layer and impedance boundaries canobscure field structures within.

At much higher frequencies, techniques such as microwave tomography(MWT) use wavelengths similar to the size of the dielectric structuresunder study. At these frequencies, waves freely propagate and take onmore ray-like characteristics. Although microwave paths can be morelinear through some structures, they typically do not deeply penetratesubjects (i.e. specimens) of interest—such as the human body—and candramatically diffract, reflect, and scatter around dielectricstructures, creating a more dynamic inverse scattering problem thanEIT/ECT, which can be more computationally demanding.

Although the scattering behaviors are different in thelow-frequency/static and microwave regimes, both generate ill-posedscattering data that cannot be definitively inverted to resolve thespatial and electrical characteristics of the scattering dielectricstructure. The data generated in both regimes can be cumbersome and timeconsuming to solve and may have multiple mathematically possiblesolutions or no solution at all.

Thus, two key problems have limited broad use of dielectric impedancetomography in three-dimensional, inhomogeneous, or complex highdielectric constant structures, such as the human body. The first is thesignificant mismatch between the dielectric characteristics of thesestructures and the surrounding air. The second is solving the inverse ofmulti-path or scattered electromagnetic waves through complexstructures—a mathematically ill-posed problem.

The impedance mismatch between differing dielectric materials severelylimits non-contact measurements because the majority of measuringelectromagnetic waves will reflect or refract from the specimen ofinterest, and wavelengths that provide reasonable spatial resolution inair (typically GHz and above) are extremely dissipative in manyhigh-dielectric-constant specimens. This limitation is currentlyaddressed by either measuring impedances through direct contact with thespecimen or performing measurements in a dielectric matching media. Suchconstraints are not practical in many situations where throughput anddisruption are concerns, such as medical trauma, security, ormanufacturing applications.

Even when spatially diverse data is obtained, solving the internalstructure of inhomogeneous dielectrics can prove intractable when theprobing electromagnetic waves are free to propagate, resonate, andinterfere with each other. Although much literature has been devoted tostudying this mathematical problem, significant computational resourcesmay be required to develop even cursory solutions.

Several techniques have been proposed for tackling the inherent issuesin dielectric impedance tomography. For example, several issued U.S.patents detail methods requiring a probe or array of probes to come intofull contact with a patient or specimen. For example, see U.S. Pat. Nos.9,042,957, 8,391,968, and 5,807,251.

Electrical impedance tomography methods that do not require specimencontact either require intermediate media or use very short wavelengthsand high powers. Electrical impedance tomography methods that do notrequire specimen contact but require intermediate media are described,for example, in several issued U.S. patents including: U.S. Pat. Nos.8,010,187, 4,135,131, 7,164,105, and 7,205,782. For example, electricalimpedance tomography methods that do not require specimen contact butuse very short wavelengths and high powers are described, for example,in several issued U.S. patents including: U.S. Pat. Nos. 8,933,837,7,660,452, and 7,664,303.

Capacitance measurement techniques or electrical capacitance tomographycan offer advantages over impedance methods using freely propagatingfields by completing a circuit between capacitor electrodes applied tothe specimen. For example, systems that inherently use lower frequenciesby constraining their propagation to the capacitor circuit forcapacitive tomographic techniques are described, for example, in severalissued U.S. patents including: U.S. Pat. Nos. 9,110,115 and 8,762,084.Although these techniques can reduce multi path complexity andattenuation of high frequencies, they require direct specimen contactand perform poorly in large or complex structures because electricfields are drawn to regions of a highest dielectric constant, loopingaround low dielectric constant regions or inhomogeneities, andpotentially obscuring features of interest.

Where the dielectric profile to be studied extends only along a singledimension, transmission line methods have been successfully used. Forexample, in U.S. Pat. Nos. 9,074,922, and 4,240,445. See also,non-patent literature: Open-wire Transmission Lines Applied to theMeasurement of the Macroscopic Electrical Properties of a Forest region,John Taylor, et al, Stanford Research Institute, October 1971; CoaxialLine Reflection Methods for Measuring Dielectric Properties ofBiological Substances at Radio and Microwave Frequencies—A Review, IEEETransactions on Instrumentation and Measurement (Volume: 29, Issue: 3,September 1980); and Electromagnetic Level Indicating (EMLI) SystemUsing Time Domain Reflectometry, William J. Harney, Christopher P.Nemarich, Oceans '83, Proceedings, 29 Aug.-1 Sep. 1983.

There exists a need, therefore, for new systems and methods fortomographing dielectric materials that generate spatially solvable dataand do not require excessively high frequencies, intermediate media, orintimate contact with the specimen under test.

Electromagnetic fields with linear or hard field characteristics wouldaddress these problems because they would yield tomographic data from aknown and defined region. It is known that in a wave propagating intransverse electric (TE) or transverse electric and magnetic (TEM)modes, the electric fields are orthogonal to the direction ofpropagation. Therefore, if an electromagnetic field is propagating in aknown direction and its propagation is determined to be in TE or TEMmode, linearity and direction of the electric fields can be assumed,creating a hard-field-like condition.

It is also known that in TE or TEM modes propagating through a media,propagation speed (V_(prop)) and impedance (Z) are related by themedia's relative permittivity or dielectric constant (ε_(r)) as acomponent of its electric permittivity (ε=ε_(r) ε₀), such that:

$\begin{matrix}{{{Impedance}(Z)} = {{\sqrt{\frac{\mu}{ɛ}}\mspace{14mu} {{Speed}\left( V_{prop} \right)}} = {{\frac{1}{\sqrt{ɛ\mu}}\mspace{14mu} V_{prop}} = \frac{1}{ɛ\; Z}}}} & (1)\end{matrix}$

where μ is the material's magnetic permeability and ε₀ is thepermittivity of free space. The above relationship holds in TEtransmission in an inhomogeneous dielectric comprised of structures thatare sufficiently small relative to the probing wavelength (or whosetraversal time comprises an insignificant fraction of the probingfrequency's period), that the dielectric behaves as a mixture orcomposite dielectric with linear contributions from the constituentdielectrics as formulated by others as:

$\begin{matrix}{ɛ_{eff} = {ɛ_{1}\left( \frac{ɛ_{2}}{ɛ_{2} - {f_{2}\left( {ɛ_{2} - ɛ_{1}} \right)}} \right)}} & (2)\end{matrix}$

where ε_(eff) is the effective dielectric constant of a mixturecomprised of a first material with dielectric constant ε₁ and a secondmaterial of dielectric constant ε₂ comprising f₂ volume fraction of themixture.

However, in an inhomogeneous dielectric with larger structures, speedand impedance may be dominated by the E of certain constituent physicalelements of the structure. For example, if the traversal time throughconstituent dielectric structures differs by more than a small fractionof the probing frequency's period, the geometries and orientation of theconstituent dielectric structures must be taken into account and theabove mix equation is no longer accurate. Analytic equations for complexstructures of significant frequency fractions in traversal time or moreare complex, not readily solved, and often do not have unique solutions.

A practical example of this phenomenon is a foamed polyethylene (PE)coaxial cable: a homogenous foamed PE dielectric creates a transmissionline (such as an RG-59 cable) of 75 Ohms and propagation velocity(V_(prop)) of 83% the speed of light. Whereas the same structurecontaining the same volume of air and PE, but concentrated into regionsof pure PE and pure air, will have regional characteristics of 60 Ohmsand 66% V_(prop) for pure PE and 90 Ohms and 99% V_(prop) for air. Ifthese bifurcated regions are aligned along the direction of propagation,the differing propagation velocities will disrupt TEM behavior and thewave will encounter significant dispersion between the slower and fasterdielectric components. From a measurement perspective, the line'simpedance (or composite ε_(eff)) and propagation velocity will be acomplex function of the probing frequencies and the PE and airconstituent geometries.

If, in the above example, the line could be restored to TE mode, theeffective dielectric constant ε_(eff) can again become a linear functionof the fraction of the constituent components such as Eq. 2 despitetheir bifurcation. This could be accomplished by inductively loading thecenter conductor of the coaxial cable to slow its velocity to match theslower solid PE constituent. An RG-63 coaxial cable is a practicalmanifestation of this behavior. By inductively loading the coreconductor, RG-63 propagates in TEM mode with a uniform 125 ohms and 81%velocity despite containing a bifurcated PE and air dielectric along thedirection of propagation.

SUMMARY

Various embodiments of the present technology include a system fordetermining characteristics of a specific region within an inhomogeneousdielectric specimen by guiding propagation of electric fields throughthe inhomogeneous dielectric specimen. In some embodiments the systemcomprises: (a) at least one source of electromagnetic energy forgenerating electromagnetic waveforms, the electromagnetic waveformscomprising electric fields propagating along a prescribed path thatdefines a series of spatial regions through which the electric fieldspropagate, the prescribed path comprising electric field modulatingelements that determine a rate of electric field propagation along theprescribed path; (b) a plurality of conductors for guiding the electricfield propagation through an inhomogeneous dielectric specimen in theprescribed path, the electric fields spanning between two or more of theplurality of conductors as the electric fields propagate along theprescribed path, the plurality of conductors being external to theinhomogeneous dielectric specimen; and (c) a plurality of measurementpoints for determining a measurement of the electric fields propagatingalong the prescribed path, the measurement of the electric fields usedto determine regional dielectric characteristics of the inhomogeneousdielectric specimen and dielectric characteristics of the specificregion within the inhomogeneous dielectric specimen.

In various embodiments the plurality of conductors for guiding theelectric field propagation through the inhomogeneous dielectric specimenin the prescribed path comprise a first conductor parallel to a secondconductor.

In some embodiments the plurality of conductors for guiding the electricfield propagation through the inhomogeneous dielectric specimen in theprescribed path comprise an array of parallel conductor pairs. Invarious embodiments each pair of the array of parallel conductor pairsare opposed on opposite sides of the inhomogeneous dielectric specimen.In some embodiments each pair of the array of parallel conductor pairsare adjacent to each other on a same side of the inhomogeneousdielectric specimen.

In various embodiments the electromagnetic waveforms along theprescribed path are sequenced across the plurality of conductors, thesequenced electromagnetic waveforms being used to create a dynamicprescribed propagation path and a dynamic rate of electric fieldpropagation.

In some embodiments the plurality of conductors for guiding the electricfield propagation through the inhomogeneous dielectric specimen in theprescribed path comprise an array of discrete conductors. In variousembodiments the electromagnetic waveforms along the prescribed path aresequenced across pairs of the array of discrete conductors, thesequenced electromagnetic waveforms used to create a dynamic prescribedpropagation path and a dynamic rate of electric field propagation.

In various embodiments the electric field modulating elements thatdetermine the rate of electric field propagation along the prescribedpath comprise physical delay structures, the physical delay structuresslowing the rate of electric field propagation along the prescribed pathand decreasing a speed of electromagnetic waves along the prescribedpath.

In some embodiments the electric field modulating elements thatdetermine the rate of electric field propagation along the prescribedpath comprise electronic components, the electronic componentscontrolling the rate of electric field propagation along the prescribedpath and controlling a speed of electromagnetic waves along theprescribed path.

In various embodiments the electric field modulating elements thatdetermine the rate of electric field propagation along the prescribedpath comprise active electronic components, the active electroniccomponents generating electric fields to screen against parasiticeffects.

In some embodiments the measurement of the electric fields propagatingalong the prescribed path measures one or more of: voltage, current,phase, and strength of the electric fields propagating along theprescribed path.

In various embodiments systems of the present technology furthercomprise: (d) at least one processor; and (e) a memory storingprocessor-executable instructions, wherein the at least one processor isconfigured to implement the following operations upon executing theprocessor-executable instructions: (i) determining an effectivedielectric constant of the specific region within the inhomogeneousdielectric specimen; (ii) determining whether the effective dielectricconstant of the specific region within the inhomogeneous dielectricspecimen is consistent with the rate of the electric field propagationalong the prescribed path; (iii) modulating the electric fieldpropagation along the prescribed path when the effective dielectricconstant of the specific region within the inhomogeneous dielectricspecimen is not consistent with the rate of the electric fieldpropagation along the prescribed path; (iv) measuring waveforms usingthe electric field propagation through the specific region within theinhomogeneous dielectric specimen; and (v) determining features of thespecific region within the inhomogeneous dielectric specimen using thewaveforms.

In some embodiments the at least one processor is further configured toimplement the following operations upon executing theprocessor-executable instructions: generating a tomograph of theinhomogeneous dielectric specimen using the features of the specificregion within the inhomogeneous dielectric specimen.

In various embodiments systems further comprise auxiliary sensors, theauxiliary sensors measuring an air gap between the plurality ofconductors and the inhomogeneous dielectric specimen in the prescribedpath.

In some embodiments the at least one processor is further configured toimplement the following operations upon executing theprocessor-executable instructions: measuring the air gap between theplurality of conductors and the inhomogeneous dielectric specimen in theprescribed path; and adjusting the determining the effective dielectricconstant of the specific region within the inhomogeneous dielectricspecimen using the measuring the air gap to increase accuracy of thedetermining the effective dielectric constant.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like reference numerals refer toidentical or functionally similar elements throughout the separateviews, together with the detailed description below, are incorporated inand form part of the specification, and serve to further illustrateembodiments of concepts that include the claimed disclosure, and toexplain various principles and advantages of those embodiments.

The methods and systems disclosed herein have been represented whereappropriate by conventional symbols in the drawings, showing only thosespecific details that are pertinent to understanding the embodiments ofthe present disclosure so as not to obscure the disclosure with detailsthat will be readily apparent to those of ordinary skill in the arthaving the benefit of the description herein.

FIGS. 1A-C illustrate the concept of a region within which the presenttechnology measures an effective dielectric constant Eeff, according tovarious embodiments of the present technology.

FIG. 2 illustrates an array of transmission line structures that definelinear rows of regions along the path of propagation of each line,according to various embodiments of the present technology.

FIG. 3 shows a grid of metallic squares over a ground plane, each squaredefining a region through a dielectric specimen, illustrating a gridpattern of regions, according to various embodiments of the presenttechnology.

FIG. 4 notionally illustrates the impedance measured through a region ofinhomogeneous dielectric as measured at various propagation speeds,according to various embodiments of the present technology.

FIGS. 5A-B illustrate the field behavior of an electromagnetic wavepassing through an inhomogeneous dielectric, according to variousembodiments of the present technology.

FIG. 6 illustrates four auxiliary sensors positioned to measure the airspace between the region-defining structures and the specimen understudy, according to various embodiments of the present technology.

FIGS. 7A-D illustrate diagrammatic views of electric fields and regionsmeasured for various screened and unscreened transmission linesaccording to embodiments of the present technology.

FIG. 8 illustrates a diagrammatic view of a system that includes atransmission line with screening plates driven by active followersaccording to embodiments of the present technology.

FIG. 9 illustrates a diagrammatic view of a system that includes aparallel transmission line structure applied to a surface of a specimenand screened by screening plates and driven by active elements accordingto embodiments of the present technology.

FIG. 10 illustrates a procedure to iteratively determine the Eeff of aspecific region from a measured impedance and propagation velocity,according to various embodiments of the present technology.

FIG. 11 illustrates the current through a transmission line structure asa pulse moves from region to region as measured by current-sensingelements, according to various embodiments of the present technology.

FIG. 12 illustrates an array of transmission line structures eachinductively loaded or designed to propagate at a different speed andthereby measure the impedance of a region at a different speed,according to various embodiments of the present technology.

FIG. 13 illustrates the conceptual layout of hardware along the lengthof a single passive transmission line, according to various embodimentsof the present technology.

FIG. 14 shows a notional sequencing that the control and analysiscomputer of FIG. 13 would issue, according to various embodiments of thepresent technology.

FIG. 15 illustrates the conceptual layout of hardware along the lengthof a single programmable transmission line, similar to the passive line,but incorporating a programmable element for each region, according tovarious embodiments of the present technology.

FIG. 16 illustrates the conceptual layout of hardware of atwo-dimensional section for fully active sequencing of fieldpropagation, according to various embodiments of the present technology.

FIG. 17 illustrates the conceptual propagation of fields across atwo-dimensional section of an active embodiment as the regional fieldssources are sequenced from left to right, according to variousembodiments of the present technology.

FIG. 18 illustrates the conceptual propagation of fields in atwo-dimensional section of an active embodiment as the regional fieldssources are sequenced in outward or radial patterns, according tovarious embodiments of the present technology.

FIG. 19 illustrates the concept of region tilting by adjusting the fieldproducing elements in an active embodiment such that the regions areangled from the lower left to upper right as they propagate into thepage, according to various embodiments of the present technology.

FIG. 20 illustrates a graph of voltage data from a specimen of solid waxgathered as a pulse moves from region to region along a transmissionline-based system according to embodiments of the present technology.

FIG. 21 illustrates a graph of voltage data from a specimen of solid waxcontaining a water cavity gathered as a pulse moves from region toregion along a transmission-line based system according to embodimentsof the present technology.

FIG. 22 illustrates a diagrammatic representation of an example machinein the form of a computing system within which a set of instructions forcausing the machine to perform any one or more of the methodologiesdiscussed herein is executed.

DETAILED DESCRIPTION

While the present technology is susceptible of embodiment in manydifferent forms, there is shown in the drawings and will herein bedescribed in detail several specific embodiments with the understandingthat the present disclosure is to be considered as an exemplification ofthe principles of the present technology and is not intended to limitthe technology to the embodiments illustrated.

In various embodiments the present technology provides a transmissionline—like apparatus that spatially and temporally guides propagation ofelectromagnetic fields through an inhomogeneous dielectric specimenwhile providing external measurements points that reveal thedielectric's internal structure.

In various embodiments the present technology involves systems andmethods to bring tractability to the dielectric impedance tomographyproblem by using external structures to guide the spatial propagation ofelectromagnetic fields, regulate their temporal velocity through aspecimen, and provide a structure for external measurement on whichinternal dielectric features will manifest. When the electromagneticfield propagation is guided by a guiding external structure—such as atransmission line—the same impedance mismatches that complicatetomographic methods using freely propagating fields reveal andcharacterize different dielectric features of the specimens becauseperturbations induced by these internal dielectric features areexternally measured along the guiding structure.

In various embodiments the present technology includes a pair ofconductors or an array of conductor pairs along which an electric fieldpropagates, with the conductors so arranged that the propagating fieldsbetween them pass through the specimen under test. The transmission lineis driven by a radio frequency (RF) or pulse probing signal source asshown, and may or may not be terminated with a known impedance. Invarious embodiments, a field guiding system includes delay means forretarding the propagation of the probing signal so that the speed ofpropagation of the probing signal matches the speed of electromagneticpropagation within the specimen under test.

The present technology creates TE-like propagation within aninhomogeneous dielectric region under study so that the effectivedielectric constant (Eeff) of the region can be accurately determined.It accomplishes this by measuring the impedance between two conductiveelements defining a region while also measuring and/or modulating thespeed at which fields propagate through the region. Thus, the Eeff of aregion is derived from two measurements: an impedance, and a propagationvelocity at which the impedance was measured.

A spatial region for study is typically defined as a columnar regionbetween two conducting plates as shown in FIGS. 1A-C. Impedance will bemeasured between the two plates, and the velocity of electromagneticpropagation through the region is determined either passively, as intransmission line-based embodiments, or in active embodiments, modulatedto a prescribed value. Regions may be aligned along lengths of paralleltransmission lines, as shown in FIG. 2, to spatially define the path forpropagation from one region to the next, or they may be physicallyseparate elements with a dynamically determined propagation pathway, asshown in FIG. 3. Propagation from region to region may be a passiveprocess as in the case of a transmission line, or an active processwhere phased drive circuits propagate fields from one region to thenext. Regions in either active or passive embodiment may be defined overa single ground plane as shown in FIGS. 2 and 3, with opposing elementsas shown in FIGS. 14 and 15, or along a single side of a specimen asshown in FIG. 9.

In either the passive or active embodiments, the present technologydetermines the Eeff within the region by calculating a value from theimpedance as measured by electronics probing voltage, current, and/orphase information for a specific region. Where the impedance is measuredby a displacement current through a region, the ε_(reff) of the regioncan be calculated as:

$\begin{matrix}{ɛ_{eff} = {\frac{I(\omega)}{{E(\omega)}\omega}\frac{d}{A}}} & (3)\end{matrix}$

Where I(ω) is the measured current at a frequency (ω) for an excitationE(ω) across a region of A area and d length. Alternative measurements ofvoltage across a region or current between regions will yield similarformulations with the premise of deriving the dielectric constant of theregion based on voltage and current measurements made.

Likewise, the V_(prop) can be taken as a function of the region's lengthin the direction of propagation and the field's transit time:

$V_{prop} = \frac{\Delta \; t}{\Delta \; d}$

Where Δt is the propagation time from region to region, either asmeasured or as actively modulated by the system, and Δd is the length ofthe region in the direction of propagation.

The impedance measured within a region will vary depending on the speedat which the probing field traverses it, as illustrated in FIG. 4. Atthe characteristic speed of the Eeff, the impedance will be at aminimum. However, if the propagation speed is faster than Eeff,impedance will increase, because the fields will not have time to fullyinteract with the slower, low-impedance dielectric components. Likewise,if the speed of propagation from region to region is too slow, impedancewill also increase, because the fields from previous regions will raceout from their intended region and undercut into the region ahead. Ingeneral, a region's impedance will be at a minimum when its speed isproperly matched to the intrinsic velocity of electromagneticpropagation of the region.

To obtain an accurate value for a region's ε_(eff), it must be measuredat multiple propagation speeds. This can be done by slowing the V_(prop)by adding inductive, electronic, or other slowing mechanisms so that theV_(prop) matches that of a region's slowest dielectric component, asshown in FIGS. 5A-B, to establish a TE mode. Additionally, slow wave ormetamaterial structures such as electronic band-gap structures can beused to delay field propagation.

In one sense, these slowing mechanisms alter the fast dielectriccomponents to form a virtual dielectric whose speed matches that of theslow dielectric component, thereby enabling a TE-like mode ofpropagation through the region. FIGS. 5A-B illustrate diagrammatic views500 of propagation of electric fields at different velocities accordingto embodiments of the present technology. FIG. 5A shows propagation ofan electric field through a transmission line running faster than avelocity of propagation in a dielectric under examination 501 (i.e.,specimen), having dielectric constant ε_(sp), thus obscuring an internalfeature of the specimen 502, having dielectric constant ε<ε_(sp). Incontrast, FIG. 5B shows propagation of an electric field when atransmission line is slowed to accommodate an effective dielectricconstant of a specimen, an internal feature of the specimen, and asurrounding air gap, thus, allowing the electric field a representativeinteraction with the dielectric. In more detail shown in FIG. 5B, thewave front through a specimen is slowed by distributed inductiveelements 505 to accommodate the ε_(eff) of the specimen, an internalfeature, and a surrounding air gap 510, thereby creating a TE-likepropagation mode and gaining a more fulsome and representative fieldinteraction with the dielectric.

The velocity or propagation through a transmission line is a function ofthe per unit length capacitance (C_(tl0)) and inductance (L_(tl0)) suchthat:

Vprop_(tl)=1/√{square root over (L _(tl0) C _(tl0))}  (4)

A transmission line's C_(tl0) is a function of line geometry and the εof its internal dielectric. The above formulation of transmission linevelocity of propagation equation (4) mirrors that of the intrinsicvelocity of a dielectric's electromagnetic propagation in equation (1),with the exception that per unit length characteristics of transmissionline propagation are determined by physical structures and can thereforebe manipulated. Therefore, by adding a per unit length inductive load orresistance L_(L0) so that:

$\begin{matrix}{{Vprop}_{t\; l} = {\frac{1}{\sqrt{\left( {L_{{tl}\; 0} + L_{L\; 0}} \right)C_{{tl}\; 0}}} \cong {Vprop}_{s}}} & (5)\end{matrix}$

where Vprop_(s) is the speed of electromagnetic propagation in thespecimen region of interest, a TE-like mode can be obtained as shown inFIG. 5B.

FIGS. 7A-D illustrates diagrammatic views 700 of electric fields andregions measured for various screened and unscreened transmission linesaccording to embodiments of the present technology. FIG. 7A shows anunscreened transmission line, FIG. 7B shows an unscreened transmissionline with an outside high ε_(r) feature 705, FIG. 7C shows an screenedcentral transmission line, and FIG. 7D shows a screened centraltransmission line with an inside high ε_(r) feature 710, according toembodiments of the present technology. In more detail, the diagrammaticviews 700 of FIGS. 7A-D show electromagnetic waves propagating on linesparallel to either side of a given line, which provide fields thatscreen or restrict the x-axis spread of a central line's fields, therebycreating a narrower or more focused region in the central line's x-axis.FIG. 7A shows an electric field (and equivalently the region measured)in an unscreened line. FIG. 7B shows an unscreened line with the outsidehigh ε_(r) feature 705. FIG. 7C shows fields in a central line screenedby parallel counterparts. FIG. 7D shows unperturbed fields of a centralline screened by parallel counterparts, one of which contains the insidehigh ε_(r) feature 710 between the parallel counterparts.

In various embodiments of the present technology a line's sensitivitymay also be directed, for example, on a single line or to limit fields'z-axis spread above or below the specimen region—through the use ofactive screening elements as shown in FIG. 8. FIG. 8 illustrates adiagrammatic view of a system 800 that includes a transmission line withscreening plates driven by active followers according to embodiments ofthe present technology. FIG. 8 shows system 800 comprising a guidestructure 805 and screening plates driven by active followers. Forexample, screening plate 815 driven by active voltage follower 810. Inthis case, active components (e.g., active voltage follower 810) measurethe voltage along the line as it changes with the propagation of a wave,and drive a plate (e.g., screening plate 815) or other radiating elementto oppose fields radiating from the line in an undesirable direction.For example, in some embodiments the electric field modulating elementsthat determine the rate of electric field propagation along theprescribed path may comprise electronic components, the electroniccomponents controlling the rate of electric field propagation along theprescribed path and controlling a speed of electromagnetic waves alongthe prescribed path. For example, in various embodiments the electricfield modulating elements that determine the rate of electric fieldpropagation along the prescribed path comprise active electroniccomponents, the active electronic components also generating electricfields to screen against parasitic effects.

FIG. 9 illustrates a diagrammatic view of a system 900 that includes aparallel transmission line structure applied to a single surface of aspecimen according to embodiments of the present technology. As inconfigurations where the parallel transmission lines are on opposingsides of the specimen, a region of characterization exists between theparallel conductors, but also extends both into the top layers of thespecimen and air above the parallel lines. For example, each pair of thearray of parallel conductor pairs may be adjacent to each other on asame side of the inhomogeneous dielectric specimen. FIG. 9 further showsactive screening plates 903 and 904 and driving elements 905 and 906applied to a parallel stripline 901 and 902 to screen the extent of theregion of characterization from extending into the air above theparallel lines. Such an embodiment is used where only one side of thespecimen is accessible or only a thin or top layer of an inhomogeneousdielectric need be characterized.

Because the present technology may not involve contact with the specimenunder study in various embodiments, accuracy may be further improved byincorporating ancillary sensors to determine the amount of air gap aboveor below the specimen within the region, as shown in FIG. 6. An air gapspace (e.g., air gap 510) within a region but external to the specimenappears essentially the same if it were internal to the specimen.Advantageously, since a surrounding air space can be readily measuredthrough other means (e.g., physical, optical, acoustical, etc.) itsimpact can be readily calculated out of the region's ε_(eff) using mixequations like those of equation 2.

A procedure for measurements to determine the ε_(eff) of a region isdescribed in FIG. 10 according to embodiments of the present technology.Propagation speed and propagation pattern can be passively,programmatically, or actively varied to fulfill the procedure describedin FIG. 10. The procedure first determines a candidate ε_(eff) throughmeasurements and calculations like those of equation 3. The candidateε_(eff) is then evaluated as to whether it is consistent with theV_(prop);

$\begin{matrix}{{{{i.e.\mspace{14mu} {whether}}\mspace{14mu} {the}\mspace{14mu} {candidate}\mspace{14mu} ɛ_{eff}} = \frac{1}{Z\mspace{14mu} V_{prop}}},{{{or}\mspace{14mu} V_{prop}} = \frac{1}{ɛ_{eff}Z}}} & (6)\end{matrix}$

If

$\begin{matrix}{{V_{prop} < \frac{1}{ɛ_{eff}Z}}\mspace{14mu}} & \;\end{matrix}$

the candidate ε_(eff) is too low and V_(prop) is decreased to obtain amore accurate candidate ε_(eff). The temporal and spatial pattern may bevaried to optimally arrive at an optimal candidate ε_(eff).Alternatively, a procedure might execute all possible combinations ofspeed and propagation pattern and then later evaluate the totality ofdata for the best candidate ε_(eff).

In a passive embodiment, several transmission lines are arrayed inparallel, as shown in FIG. 2, in order to laterally define rows ofregions across the span of parallel transmission lines as shown in FIGS.7C and 7D according to various embodiments. Regions are defined in thedirection of propagation by points of measurement along the length ofeach line. The lines are driven by a radio frequency (RF) or pulsesource probing signal and may or may not be terminated with a knownimpedance. As the RF or pulse signal propagates down the line, impedancechanges will be revealed via voltage or current measurements on thesurface of the line as shown in FIG. 11. Although these impedancechanges will reveal the spatial location of dielectric structures, theymay not fully reveal the ε_(eff) of a specific region because thestructures may have induced a non-TEM mode within the line, such as thatshown in FIG. 5A. Obtaining measurements at points along the surface ofthe line which reveal impedance changes may be important to resolvingthe spatial uncertainty that arises from merely time domainreflectometry methods, where measurements made through an end portcannot disambiguate a short section of slow velocity dielectric from along section of high velocity dielectric.

Passive line data at additional speeds can be obtained by inductivelyloading or altering an array of lines with slow wave structures as shownin FIG. 5B and equation 5. A further embodiment of FIG. 5B that affordsa variety of propagation speeds is the array of parallel transmissionlines shown in FIG. 12. Each line is structured to have a slightlydifferent propagation velocity. The array is mechanically passed overthe specimen and impedance data for each region is gathered when scannedby each line of different velocity. Comparing impedance data from linesof various speeds as they passed over the same physical region of thespecimen can identify the minimum impedance value that matches apropagation velocity per equation 6 above.

Impedance is measured from each region of the passive embodiment via avoltage and/or current probe within the region according to variousembodiments. Impedance is then calculated via Ohm's law by knowing thedrive signal or signal from the previous adjacent region. The candidateε_(eff) is then calculated from the impedance of the line based on thephysical bounds of the region and any added inductive or slowingstructures. FIG. 13 shows the hardware of a preferred embodiment using acurrent sensor between regions. FIG. 14 shows a process for operationusing a current sensor between regions as orchestrated by a controllingcomputer. The speed and impedance data generated by a single-speed line,as illustrated in FIG. 13, may be stored by the computer for comparisonagainst speed and impedance data from varying speed lines, such as thosefrom FIG. 12, to determine the optimal fit for ε_(eff).

An extension of the passive embodiment is a programmable embodimentwhere the inductive or delay elements between regions along a line canbe altered or programmed to tune the line to a different speed, asillustrated in FIG. 12. A delay element, such as an inductor orprogrammable delay line, may be switched on or its characteristicsaltered as instructed by the control computer. For example, the electricfield modulating elements that determine the rate of electric fieldpropagation along the prescribed path may comprise physical delaystructures, the physical delay structures slowing the rate of electricfield propagation along the prescribed path and decreasing a speed ofelectromagnetic waves along the prescribed path.

In an active embodiment, field propagation from region to region iscontrolled by electronics and not free propagation as in the passiveembodiment. Each region contains its own probing signal sourcecontrollable by a control and analyzing computer, as well as mechanismsfor impedance measurement and/or waveform capture. In the activeembodiment, the rate and direction of propagation from region to regionis determined by a control and analyzing computer and may be dynamicallyor iteratively altered to determine a regions' ε_(eff).

Active regions may be defined by plates in a grid, hexagonal, arcs, orother repeating pattern as suited to the application. The propagationfrom region to region may likewise be altered to suit the application.Detection of boundaries between dielectric structures can be clearerwhen propagating from lower ε to higher ε, and propagation paths arenormal to boundaries. Thus, a sophisticated active embodimentdynamically alters propagation paths and patterns to discern finerdetail. For example, regions could propagate in one direction and thenback, propagate radially or concentrically, diagonally across thescanning plane, or alternated or phased in a checkerboard pattern asshown in FIG. 18. In an active embodiment, propagation may be originatedand terminated at various points. Active propagation also eliminates theneed for mechanical operations, such as sweeping the varied speed linesembodiment of FIG. 12 or reorienting the specimen, to gather fulltomographic data.

All embodiments generate an ε_(eff) of a columnar region which may stillcontain multiple dielectric components in the axis of the column. Toresolve this uncertainty and generate a full tomographic rendering, datamust be gathered from an orthogonal axis. In passive embodiments, thiscan be done by reorienting either the specimen or passive lines. In atwo-sided active embodiment, alternate region axes can be obtained bytilting the regions through slight phasing of the top and bottom platesof the cell and/or creating a screening field though adjacent regionplates as shown in FIG. 19, so long as the tilted region stillapproximates TE in the direction of propagation.

Those skilled in the art will appreciate that numerous modifications andvariations may be made to the above disclosed embodiments withoutdeparting from the spirit and scope of the present invention.

FIGS. 1A-C illustrate the concept of a region within which the presenttechnology measures an effective dielectric constant (ε_(eff)).Impedance through the region is indicated by currents passing verticallywhile fields are propagating to the right as depicted in FIG. 1, FIG.1B, and FIG. 1C illustrate this conceptual region within transmissionline structures in two dimensions and three dimensions, respectively.For example, the plurality of conductors for guiding the electric fieldpropagation through the inhomogeneous dielectric specimen in theprescribed path may comprise a first conductor parallel to a secondconductor.

FIG. 2 illustrates an array of transmission line structures that definelinear rows of regions along the path of propagation of each line. Forexample, the plurality of conductors for guiding the electric fieldpropagation through the inhomogeneous dielectric specimen in theprescribed path may comprise an array of parallel conductor pairs. Insome embodiments each pair of the array of parallel conductor pairs areopposed on opposite sides of the inhomogeneous dielectric specimen.

FIG. 3 shows a grid of metallic squares over a ground plane, each squaredefining a region through a dielectric specimen, illustrating a gridpattern of regions. The grid of FIG. 3 depicts a lumped or segmentedversion of the continuous lines of FIG. 2. Adding connective elementsbetween the squares in the vertical direction would allowelectromagnetic fields to propagate from region to region vertically.Adding horizontal connective elements would allow fields to propagatehorizontally, akin to the lines in FIG. 2.

FIG. 4 notionally illustrates the impedance measured through a region ofinhomogeneous dielectric as measured at various propagation speeds.Where the propagation from region to region is too slow relative to theintrinsic of the dielectric, the impedance of the measured region ishigh due to undercutting of fields from earlier, adjacent regions. Wherethe propagation is fast, the impedance is again high because the fieldsdo not have time to penetrate slower dielectric components.

FIGS. 5A-B illustrate the field behavior of an electromagnetic wavepassing through an inhomogeneous dielectric. In FIG. 5A, the wave ismoving at a velocity in excess of the propagation velocity of the slowerdielectric component. In FIG. 5B, the transmission line structure hasbeen slowed to allow the wave to propagate in a transverse electric (TE)mode.

In FIG. 5A, propagation of an electric field through a transmission isline running faster than a velocity of propagation in a dielectric underexamination, thus obscuring an internal feature of the specimen. Incontrast, FIG. 5B shows propagation of an electric field when atransmission line is slowed to accommodate an effective dielectricconstant (ε_(eff)) of the dielectric under examination 501 (i.e.,specimen), an internal feature of the specimen 502, and a surroundingair gap 510, thus allowing the electric field a representativeinteraction with the dielectric.

FIG. 6 illustrates four auxiliary sensors 600 positioned to measure airspace between the region-defining structures and the subject 610 (i.e.,specimen) under study. The auxiliary sensors may operate by radar,infrared, ultrasound, or optical/video means to quantify the amount ofair space between the specimen and the region-defining structures. Invarious embodiments, the auxiliary sensors measure an air gap betweenthe plurality of conductors and the inhomogeneous dielectric specimen inthe prescribed path.

FIG. 10 illustrates a procedure to iteratively determine the ε_(eff) ofa specific region from a measured impedance and propagation velocity.

FIG. 11 illustrates the current through a transmission line structure asa pulse moves from region to region as measured by current-sensingelements 1100. FIG. 11 illustrates a diagrammatic view of measured pulsecurrent waveforms in a system according to embodiments of the presenttechnology. FIG. 11 shows pulse current waveforms 1103 as measured atpoints along the length of a first conductor 1105 and second conductor1110. The first conductor 1105 and the second conductor 1110 encompass aspecimen 1115 undergoing test that includes features of a lesserdielectric constant 1120 and features of a greater dielectric constant1125 relative to a dielectric constant of the specimen 1115.

FIG. 11 also shows pulse current waveforms 1103 that have a lowercurrent illustrating a valley 1130 on the pulse current waveforms 1103corresponding with the features of lesser dielectric constant 1120. Incontrast, pulse current waveforms 1103 have a higher voltageillustrating a peak 1135 on the pulse current waveforms 1103corresponding with the features of greater dielectric constant 1125.

FIG. 12 illustrates an array of transmission line structures eachinductively loaded or designed to propagate at a different speed andthereby measure the impedance of a region at a different speed. Such anarray is passed over a specimen 1200 (i.e., specimen) under study asshown by direction 1210 to measure the same region of the specimen underlines of different speeds. For example, the electromagnetic waveformsalong the prescribed path are sequenced across each pair of the array ofparallel conductor pairs, the sequenced electromagnetic waveforms may beused to create a dynamic prescribed path for electric field propagation.

FIG. 13 illustrates the conceptual layout of hardware along the lengthof a single passive transmission line. Each region is defined by currentsensing elements, and each current sensing element is multiplexed with amultiplexing device (MUX) into an analog-to-digital converter (ADC)which then transmits the data into a controlling and analyzing computer.

FIG. 14 shows a notional sequencing that the control and analysiscomputer of FIG. 13 would issue. It first selects a region to beacquired with a multiplexing device, then instructs the RF source toissue the drive signal, then acquires both the signal and drive, thenanalyzes the data.

FIG. 15 illustrates the conceptual layout of hardware along the lengthof a single programmable transmission line, similar to the passive line,but incorporating a programmable element for each region.

FIG. 16 illustrates the conceptual layout of hardware of atwo-dimensional section for fully active sequencing of fieldpropagation.

FIG. 17 illustrates the conceptual propagation of fields across atwo-dimensional section of an active embodiment as the regional fieldssources are sequenced from left to right.

FIG. 18 illustrates the conceptual propagation of fields in atwo-dimensional section of an active embodiment as the regional fieldssources are sequenced in outward or radial patterns.

FIG. 19 illustrates the concept of region tilting by adjusting the fieldproducing elements in an active embodiment such that the regions areangled from the lower left to upper right as they propagate into thepage in direction 1905.

FIG. 20 illustrates a graph 2000 of topographic data from a specimen ofsolid wax (ε_(r)=2.2) generated using a system according to embodimentsof the present technology. In contrast to FIG. 21, no valley or peak isshown as pulse voltage is measured in regions spanning the specimen ofsolid wax. The slight upward ramping of successive pulse heights is dueto instrumentation error.

FIG. 21 illustrates a graph 2100 of topographic data from a specimen ofwax containing an embedded water cavity (ε_(r)=80) generated using asystem according to embodiments of the present technology. As describedin FIG. 11, pulse current waveforms are measured at points along thelength of a first conductor 1105 and second conductor 1110. FIG. 11 alsoshows pulse current waveforms 1103 that have a lower currentillustrating the valley 1130 on the pulse current waveforms 1103corresponding with the features of lesser dielectric constant 1120.Similarly, the pulse voltage waveforms of FIG. 21 show a valley 2105indicating a water cavity of higher dielectric in the specimen for thesame reasons of the valley 1130 of FIG. 11.

FIG. 22 is a diagrammatic representation of an example machine in theform of a computer system 1, within which a set of instructions forcausing the machine to perform any one or more of the methodologiesdiscussed herein may be executed. For example, programming a propagationvelocity or pattern to iteratively refine data. In various exampleembodiments, the machine operates as a standalone device or may beconnected (e.g., networked) to other machines. In a networkeddeployment, the machine may operate in the capacity of a server or aclient machine in a server-client network environment, or as a peermachine in a peer-to-peer (or distributed) network environment. Themachine may be a personal computer (PC), an embedded computer, a fieldprogrammable gate array (FPGA), an application specific integratedcircuit (ASIC), a tablet PC, a cellular telephone, a portable mediadevice (e.g., a portable hard drive audio device such as an MovingPicture Experts Group Audio Layer 3 (MP3) player), a web appliance, anetwork router, switch or bridge, or any machine capable of executing aset of instructions (sequential or otherwise) that specify actions to betaken by that machine. Further, while only a single machine isillustrated, the term “machine” shall also be taken to include anycollection of machines that individually or jointly execute a set (ormultiple sets) of instructions to perform any one or more of themethodologies discussed herein.

The example computer system 1 includes a processor or multipleprocessor(s) 5 (e.g., a central processing unit (CPU), a graphicsprocessing unit (GPU), or both), and a main memory 10 and static memory15, which communicate with each other via a bus 20. The computer system1 may further include a video display 35 (e.g., a liquid crystal display(LCD)). The computer system 1 may also include an alpha-numeric inputdevice(s) 30 (e.g., a keyboard), a cursor control device (e.g., amouse), a voice recognition or biometric verification unit (not shown),a drive unit 37 (also referred to as disk drive unit), a signalgeneration device 40 (e.g., a speaker), a network interface device 45,and dielectric measurement hardware 60. The computer system 1 mayfurther include a data encryption module (not shown) to encrypt data.

The disk drive unit 37 includes a computer or machine-readable medium 50on which is stored one or more sets of instructions and data structures(e.g., instructions 55) embodying or utilizing any one or more of themethodologies or functions described herein. The instructions 55 mayalso reside, completely or at least partially, within the main memory 10and/or within the processor(s) 5 during execution thereof by thecomputer system 1. The main memory 10 and the processor(s) 5 may alsoconstitute machine-readable media.

The instructions 55 may further be transmitted or received over anetwork via the network interface device 45 utilizing any one of anumber of well-known transfer protocols (e.g., Hyper Text TransferProtocol (HTTP)). While the machine-readable medium 50 is shown in anexample embodiment to be a single medium, the term “computer-readablemedium” should be taken to include a single medium or multiple media(e.g., a centralized or distributed database and/or associated cachesand servers) that store the one or more sets of instructions. The term“computer-readable medium” shall also be taken to include any mediumthat is capable of storing, encoding, or carrying a set of instructionsfor execution by the machine and that causes the machine to perform anyone or more of the methodologies of the present application, or that iscapable of storing, encoding, or carrying data structures utilized by orassociated with such a set of instructions. The term “computer-readablemedium” shall accordingly be taken to include, but not be limited to,solid-state memories, optical and magnetic media, and carrier wavesignals. Such media may also include, without limitation, hard disks,floppy disks, flash memory cards, digital video disks, random accessmemory (RAM), read only memory (ROM), and the like. The exampleembodiments described herein may be implemented in an operatingenvironment comprising software installed on a computer, in hardware, orin a combination of software and hardware.

One skilled in the art will recognize that the Internet service may beconfigured to provide Internet access to one or more computing devicesthat are coupled to the Internet service, and that the computing devicesmay include one or more processors, buses, memory devices, displaydevices, input/output devices, and the like. Furthermore, those skilledin the art may appreciate that the Internet service may be coupled toone or more databases, repositories, servers, and the like, which may beutilized in order to implement any of the embodiments of the disclosureas described herein.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an image, tomograph, or analytic product derived fromsaid image or tomograph, or constituent data thereof includinginstructions which implement the function/act specified in the flowchartand/or block diagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

In the description, for purposes of explanation and not limitation,specific details are set forth, such as particular embodiments,procedures, techniques, etc. in order to provide a thoroughunderstanding of the present technology. However, it will be apparent toone skilled in the art that the present technology may be practiced inother embodiments that depart from these specific details.

While specific embodiments of, and examples for, the system aredescribed above for illustrative purposes, various equivalentmodifications are possible within the scope of the system, as thoseskilled in the relevant art will recognize. For example, while processesor steps are presented in a given order, alternative embodiments mayperform routines having steps in a different order, and some processesor steps may be deleted, moved, added, subdivided, combined, and/ormodified to provide alternative or sub-combinations. Each of theseprocesses or steps may be implemented in a variety of different ways.Also, while processes or steps are at times shown as being performed inseries, these processes or steps may instead be performed in parallel,or may be performed at different times.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. The descriptions are not intended to limit the scope of thepresent technology to the particular forms set forth herein. To thecontrary, the present descriptions are intended to cover suchalternatives, modifications, and equivalents as may be included withinthe spirit and scope of the present technology as appreciated by one ofordinary skill in the art. Thus, the breadth and scope of a preferredembodiment should not be limited by any of the above-described exemplaryembodiments.

What is claimed is:
 1. A system for determining characteristics of aspecific region within an inhomogeneous dielectric specimen by guidingpropagation of electric fields through the inhomogeneous dielectricspecimen, the system comprising: at least one source of electromagneticenergy for generating electromagnetic waveforms, the electromagneticwaveforms comprising electric fields propagating along a prescribed paththat defines a series of spatial regions through which the electricfields propagate, the prescribed path comprising electric fieldmodulating elements that determine a rate of electric field propagationalong the prescribed path; a plurality of conductors for guiding theelectric field propagation through an inhomogeneous dielectric specimenin the prescribed path, the electric fields spanning between two or moreof the plurality of conductors as the electric fields propagate alongthe prescribed path, the plurality of conductors being external to theinhomogeneous dielectric specimen; and a plurality of measurement pointsfor determining a measurement of the electric fields propagating alongthe prescribed path, the measurement of the electric fields used todetermine regional dielectric characteristics of the inhomogeneousdielectric specimen and dielectric characteristics of the specificregion within the inhomogeneous dielectric specimen.
 2. The system ofclaim 1, wherein the plurality of conductors for guiding the electricfield propagation through the inhomogeneous dielectric specimen in theprescribed path comprise a first conductor parallel to a secondconductor.
 3. The system of claim 1, wherein the plurality of conductorsfor guiding the electric field propagation through the inhomogeneousdielectric specimen in the prescribed path comprise an array of parallelconductor pairs.
 4. The system of claim 3, wherein each pair of thearray of parallel conductor pairs are opposed on opposite sides of theinhomogeneous dielectric specimen.
 5. The system of claim 3, whereineach pair of the array of parallel conductor pairs are adjacent to eachother on a same side of the inhomogeneous dielectric specimen.
 6. Thesystem of claim 1, wherein the electromagnetic waveforms along theprescribed path are sequenced across the plurality of conductors, thesequenced electromagnetic waveforms being used to create a dynamicprescribed propagation path and a dynamic rate of electric fieldpropagation.
 7. The system of claim 1, wherein the plurality ofconductors for guiding the electric field propagation through theinhomogeneous dielectric specimen in the prescribed path comprise anarray of discrete conductors.
 8. The system of claim 7, wherein theelectromagnetic waveforms along the prescribed path are sequenced acrosspairs of the array of discrete conductors, the sequenced electromagneticwaveforms used to create a dynamic prescribed propagation path and adynamic rate of electric field propagation.
 9. The system of claim 1,wherein the electric field modulating elements that determine the rateof electric field propagation along the prescribed path comprisephysical delay structures, the physical delay structures slowing therate of electric field propagation along the prescribed path anddecreasing a speed of electromagnetic waves along the prescribed path.10. The system of claim 1, wherein the electric field modulatingelements that determine the rate of electric field propagation along theprescribed path comprise electronic components, the electroniccomponents controlling the rate of electric field propagation along theprescribed path and controlling a speed of electromagnetic waves alongthe prescribed path.
 11. The system of claim 1, wherein the electricfield modulating elements that determine the rate of electric fieldpropagation along the prescribed path comprise active electroniccomponents, the active electronic components generating electric fieldsto screen against parasitic effects.
 12. The system of claim 1, whereinthe measurement of the electric fields propagating along the prescribedpath measures one or more of: voltage, current, phase, and strength ofthe electric fields propagating along the prescribed path.
 13. Thesystem of claim 1, further comprising: at least one processor; and amemory storing processor-executable instructions, wherein the at leastone processor is configured to implement the following operations uponexecuting the processor-executable instructions: determining aneffective dielectric constant of the specific region within theinhomogeneous dielectric specimen; determining whether the effectivedielectric constant of the specific region within the inhomogeneousdielectric specimen is consistent with the rate of the electric fieldpropagation along the prescribed path; modulating the electric fieldpropagation along the prescribed path when the effective dielectricconstant of the specific region within the inhomogeneous dielectricspecimen is not consistent with the rate of the electric fieldpropagation along the prescribed path; measuring waveforms using theelectric field propagation through the specific region within theinhomogeneous dielectric specimen; and determining features of thespecific region within the inhomogeneous dielectric specimen using thewaveforms.
 14. The system of claim 13, wherein the at least oneprocessor is further configured to implement the following operationsupon executing the processor-executable instructions: generating atomograph of the inhomogeneous dielectric specimen using the features ofthe specific region within the inhomogeneous dielectric specimen. 15.The system of claim 13, further comprising auxiliary sensors, theauxiliary sensors measuring an air gap between the plurality ofconductors and the inhomogeneous dielectric specimen in the prescribedpath.
 16. The system of claim 15, wherein the at least one processor isfurther configured to implement the following operations upon executingthe processor-executable instructions: measuring the air gap between theplurality of conductors and the inhomogeneous dielectric specimen in theprescribed path; and adjusting the determining the effective dielectricconstant of the specific region within the inhomogeneous dielectricspecimen using the measuring the air gap to increase accuracy of thedetermining the effective dielectric constant.
 17. A system fordetermining characteristics of a specific region within an inhomogeneousdielectric specimen by guiding propagation of electric fields throughthe inhomogeneous dielectric specimen, the system comprising: at leastone source of electromagnetic energy for generating electromagneticwaveforms, the electromagnetic waveforms comprising electric fieldspropagating along a prescribed path that defines a series of spatialregions through which the electric fields propagate, the prescribed pathcomprising electric field modulating elements that determine a rate ofelectric field propagation along the prescribed path; a plurality ofconductors for guiding the electric field propagation through aninhomogeneous dielectric specimen in the prescribed path, the electricfields spanning between two or more of the plurality of conductors asthe electric fields propagate along the prescribed path, the pluralityof conductors being external to the inhomogeneous dielectric specimen; aplurality of measurement points for determining a measurement of theelectric fields propagating along the prescribed path, the measurementof the electric fields used to determine regional dielectriccharacteristics of the inhomogeneous dielectric specimen and dielectriccharacteristics of the specific region within the inhomogeneousdielectric specimen; at least one processor; and a memory storingprocessor-executable instructions, wherein the at least one processor isconfigured to implement the following operations upon executing theprocessor-executable instructions: determining an effective dielectricconstant of the specific region within the inhomogeneous dielectricspecimen; determining whether the effective dielectric constant of thespecific region within the inhomogeneous dielectric specimen isconsistent with the rate of the electric field propagation along theprescribed path; modulating the electric field propagation along theprescribed path when the effective dielectric constant of the specificregion within the inhomogeneous dielectric specimen is not consistentwith the rate of the electric field propagation along the prescribedpath; generating waveforms using the electric field propagation throughthe specific region within the inhomogeneous dielectric specimen; anddetermining features of the specific region within the inhomogeneousdielectric specimen using the waveforms.
 18. The system of claim 17,wherein the electric field modulating elements that determine the rateof electric field propagation along the prescribed path comprisephysical delay structures, the physical delay structures slowing therate of electric field propagation along the prescribed path anddecreasing a speed of electromagnetic waves along the prescribed path.19. The system of claim 17, wherein the electric field modulatingelements that determine the rate of electric field propagation along theprescribed path comprise electronic components, the electroniccomponents controlling the rate of electric field propagation along theprescribed path and controlling a speed of electromagnetic waves alongthe prescribed path.
 20. A system for determining characteristics of aspecific region within an inhomogeneous dielectric specimen by guidingpropagation of electric fields through the inhomogeneous dielectricspecimen, the system comprising: at least one source of electromagneticenergy for generating electromagnetic waveforms, the electromagneticwaveforms comprising electric fields propagating along a prescribed paththat defines a series of spatial regions through which the electricfields propagate; a plurality of conductors for guiding the electricfield propagation through an inhomogeneous dielectric specimen in theprescribed path, the electric fields spanning between two or more of theplurality of conductors as the electric fields propagate along theprescribed path, the plurality of conductors being external to theinhomogeneous dielectric specimen; and auxiliary sensors, the auxiliarysensors measuring an air gap between the plurality of conductors and theinhomogeneous dielectric specimen in the prescribed path.
 21. The systemof claim 20, wherein the prescribed path comprises electric fieldmodulating elements that determine a rate of electric field propagationalong the prescribed path.
 22. The system of claim 20, furthercomprising a plurality of measurement points for determining ameasurement of the electric fields propagating along the prescribedpath, the measurement of the electric fields used to determine regionaldielectric characteristics of the inhomogeneous dielectric specimen anddielectric characteristics of the specific region within theinhomogeneous dielectric specimen.